FR3044942A1 - BLASTING DEVICE FOR GRAVITY FOUNDRY - Google Patents

Abstract

The subject of the invention is a coring device for gravity casting, said coring device comprising: - means for constituting the cores comprising tools defining molding cavities, - supply means for powdery compound (s) ( s) of said cavities by feed openings, and - drying means of the cores being formed in said cavities by blowing a fluid through blow openings, such that the blow openings are distinct from the openings of food.

Description

BLASTING DEVICE FOR GRAVITY FOUNDRY

The invention relates to a foundry technique, called gravity casting, also referred to as gravity casting, which can mold metal parts. Gravity casting has several variants of implementation, including for example gravity casting called shell, source, tilted or low pressure, the invention is interested in all these variants.

The invention is more particularly concerned with so-called coring devices for making cores for molds used in this type of technique. In the foundry, the cores are, in a known manner, components of the mold, made from sand, natural or artificial, (silica, mullite, ceramic and the like, ...) which make it possible to make the internal recesses of the workpiece. mold, or undercut areas thereof.

These coring devices generally consist of three large parts, movable relative to each other.

There is first of all the upstream part, also called "firing head", which has an enclosure that receives at the top of the sand or, more generally sand associated with components of the organic binder type or mineral, for example a binder (s) in pulverulent form, coming from a hopper, and which distributes this powder mixture through at least one plate pierced with openings called "firing plate" by distribution nozzles called firing nozzles.

Then there is the "core box", which delimits the cavities that will correspond to the shape and dimensions of the cores to be manufactured, the firing nozzles mentioned above being in fluid connection with openings disposed in the upper part. cavities in question to allow filling.

There is, finally, the "drying (by a gas)" part, which allows, once the cavities of the stone box filled with the powder mixture, to harden it, so that the box The cores can finally eject hardened / compact and manipulable cores from its cavities to the molds. This hardening is done by heating the powder mixture, which causes its dehydration and hardening of the binder, for example by crosslinking when the binder is of organic type, thus ensuring the consistency of the cores.

Generally, this hardening by heating is by diffusion, heart, in the powder mixture of hot air and dry under pressure: after feeding the cavities sand / binder mixture through openings in the cavities, it comes blowing hot air through these same openings in the cavities on the nuclei being formed.

However, we seek to change the way in which the hardening of the cores is performed for different reasons. One reason is that the heating method described above has a significant energy cost. In addition, the heating operation is quite long, and significantly lengthens the production cycle time of the cores. Finally, we tend to have more and more recourse to inorganic binders, and no longer organic, especially to follow the regulatory changes in the field, and with this type of binder, improve the drying efficiency is important.

The invention therefore aims to improve the coring devices, and, more particularly, to improve the manner of operating the hardening of the cores, in particular to overcome the disadvantages mentioned above.

The invention therefore relates to a cored casting device for gravity casting, said coring device comprising: - means for constituting cores comprising tools defining molding cavities, - compound supply means ( s) powder (s) of said cavities through feed openings, and - drying means of the cores being formed in said cavities by blowing a fluid through blow openings, such that the blow openings are distinct supply openings.

The invention therefore proposes to differentiate the sand supply openings and binder hot air (fluid) blowing openings, which opens up completely new possibilities of operating the drying of the cores. Indeed, in the case of a binder hardening by heating / dehydration, the drying of the cores is obtained by the combination of the temperature of the metal tooling ("peripheral" hardening) and the circulation of a hot fluid under pressure that passes through the porous core (hardening "at heart"): the hot tool and the hot fluid vaporize and evacuate the water contained in the binder. This dehydration of the binder contained in the core makes it harden and makes it possible to obtain a hard and manipulable core (sand + binder). Dehydration can be obtained by two physical phenomena, namely the phase change from the liquid water to the steam water, the vapor water being evacuated by the gas flow, and, in the case of air as fluid drying, the absorption of moisture in dry air.

However, in the existing state of the art, the drying fluid is introduced through the same orifice that allows to inject, at first, sand in the metal tool and then the hot drying fluid. It is evacuated through openings equipped with filters arranged in the tooling in the opposite part of the tooling to the part where it is injected, the filters (for example of metal type slats) letting a fluid pass but not the sand. But the dehydration of a nucleus is a long manufacturing step to realize, if one makes the comparison with other technologies of coring (of the phenolic cold box type, ...). The coring processes, which implement a hardening of the core by drying the binder, thus have a generally very long cycle time compared to other processes, the cycle time being directly related to the ability of the process to remove water contained in the kernel. The management of the flow of the hot fluid which passes through and dries the core is therefore very important in obtaining a short cycle time.

The disadvantages of the methods according to the state of the art are therefore as follows: - The injection of the drying fluid is located opposite the kernel ejection zone. The kernel area located on the ejection side is thus dried last. It thus acquires mechanical characteristics last and therefore does not allow fast ejection of the core without risk of breakage. (Note, however, that an ejection of the core even partially dried is possible if the core supports to be ejected and manipulated, because the core continues to dry out of the tool because of its own heat), - the nozzles sand injection are dimensioned primarily so as to obtain a good filling of the sand + binder mixture, the goal being to obtain a good quality core, without poorly filled zone or insufficiently compacted, these defects on cores causing defects on the part foundry that will be cast. The injection nozzles are therefore not dimensioned optimally for the injection of the drying fluid of the binder. Areas of the core may therefore not be dried properly / sufficiently by the circulation of hot fluid. The drying is then carried out by heat conduction, which therefore lengthens the drying cycle time, [0014] The invention, by choosing in the cavities the different sand and binder feed openings of the openings for the blowing drying fluid, allows to separately improve the injection of sand and that of fluid, freeing itself from the constraints associated with the step of filling the cavities with sand: one can finally improve the way of blowing the fluid of drying through the core without the risk of degrading at the same time the way to inject the mixture sand + binder. It is thus possible, in particular, to use blowing means appropriately sized for a hot fluid, one can also freely choose the distribution and sizing of the openings for blowing the cavities, independently of the sand supply openings.

Finally, as detailed below, it is possible to choose pathways of the hot fluid in the cores from the blow openings completely different from the path of the sand + binder mixture when filling the cavities, in particular by choosing flow in the opposite direction, which speeds up drying and facilitates the ejection of the cores.

Preferably, the blowing openings are in fluid connection with a fluid supply box. The box is generally itself sealed to a hot-air or superheated steam generator, and the supply of fluid at the desired temperature and pressure in the box can be controlled by means of appropriate control means.

In this case, according to one embodiment, the box comprises a plate provided with openings in fluid connection with the blowing openings by ducts. These conduits thus pass, in particular, one of the cavities defining imprints, including the lower footprint.

Advantageously, the blow openings are equipped with filter (s). This prevents the presence of these openings disturbing the filling of the cavities by sand + binder mixture through the feed nozzles (the sand can not pass through these filters). It is thus easier to position the drying fluid injection zones in the cavities without negative impact, without any additional appearance defects on the core and thus on the final casting. These filters also help to homogenize the circulation of drying fluid in the core.

The blowing apertures and the feed openings may be arranged relative to one another in the cavities so that the direction of introduction of the powdery materials into said cavities is substantially opposite to the direction of introduction. drying fluid in said cavities.

Preferably, all the blowing openings are grouped on one edge of the cavity, and all the feed openings on an opposite edge. Specifically, when the cavities are formed by two half-molds, also called fingerprints, the feed openings may all be on the side of one of the imprints (the upper particular) and the blowing openings on the side of the other imprint ( the lower particular). This configuration allows a flow of sand in the cavity substantially in the opposite direction of the circulation of the drying fluid, later in the core being formed.

The drying means may comprise means for evacuating the fluid from the cavities by discharge openings in fluid connection with a box, possibly connected to a suction system. Providing suction makes it possible to facilitate and better control the flow of the drying fluid in the porous core.

Preferably, the evacuation openings are in fluid connection with a fluid evacuation box, the evacuation box preferably comprising a plate provided with openings in fluid connection with the evacuation openings by means of ducts or by evacuation nozzles. The discharge nozzles mounted on a plate can be placed above the feed openings, instead of the feed nozzles, during the blowing step.

[0023] Preferably, these evacuation means are equipped with filters. Again, the filters serve to contain the sand + binder mixture in the cavity, during the filling of the cavity and throughout the formation of the core.

More preferably, the evacuation means use recess feeding apertures and / or separate openings, preferably provided with filters.

According to a variant, the device according to the invention may have at least two systems for ejecting hardened cores, including in particular a system disposed on the side of the blowing openings and a system disposed on the side of the cavity supply openings. . Indeed, in known manner, there is provided a core ejection system, generally disposed on the opposite side of the core box to the side provided with sand + binder feed nozzles. According to the invention, it can be provided that the ejection system is rather on the same side, therefore, according to the preferred embodiment of the invention, on the side opposite to that of the blow openings, or to cumulate the two systems of ejection, adding this additional ejection system.

Preferably, the pulverulent compounds comprise sand and at least one mineral-type binder. Advantageously, they contain only binders of a mineral nature, for example based on silicate and / or phosphate. In fact, giving up organic binders makes it possible to follow regulatory developments in the field of foundry.

The drying fluid is preferably air (hot and dry) or superheated steam.

The invention also relates to the method of implementation of the device described above, where the pulverulent compound (s) is fed (s) the cavities by feeding openings, then where we blow a fluid in the cavities for drying nuclei being formed in said cavities by blowing a fluid through openings, the injection of the fluid into the cavities in a direction opposite to the injection of the pulverulent compounds.

[0029] Conventionally, the supply of sand and binder is generally above the core box, with the feed openings disposed on the upper edge of the cavities. According to the invention, the blowing apertures are rather arranged on the lower edge of the cavities, so that the sand and binder core box is fed in a direction generally from top to bottom, and in that then blows hot fluid in a generally opposite direction, from bottom to top.

According to one embodiment, the drying fluid is removed from the cavities with suction through openings in said cavities. It forces the evacuation of the fluid out of the cavities, which allows to accelerate and better guide its path in the porous core.

The invention also relates to the application of the device and / or the method described above for obtaining foundry cores devoid of organic binder.

The invention also relates to the application of the device and / or method described above for obtaining foundry cores corresponding to portions of engine parts, including cylinder head portions, and for example engine cylinder head water chambers, and all other castings, in particular intended for the automotive industry, whose geometry must be very precise and reproducible and whose surface quality must be high.

The invention also relates to the cores obtained by the device described above, these cores being substantially free of organic components.

The invention also relates to a foundry casting process gravity castings, which uses these cores.

Other features and advantages will appear on reading the description below of a particular embodiment, not limiting of the invention, with reference to the following very schematic figures: • Figures 1 to 6 represent as a whole, in vertical section, an example of a coring device according to the state of the art existing, Figure 1 being an overview with the open core box, Figures 2 to 6 showing the device to different stages of nucleus production; • Figure 7 is a vertical sectional view of a modified coring device according to a first variant of the invention; • Figure 8 is an enlargement of the hot air injection plate of the coring device of Figure 7; • Figure 9 is a vertical sectional view of a modified coring device according to a second variant of the invention.

These figures are very simplified, the elements shown are not necessarily scaled with respect to each other or from one figure to another. Each reference retains the same meaning from one figure to another. The representation of the tools is done in their usual configuration of use, and it is in this sense that one must understand the spatial references of the type "superior", "inferior", "high" or "low". .. (as well as throughout this text).

Figures 1 to 6 are views in vertical section of a device 1 coring according to the state of the art, and all compounds and the mode of operation will not be detailed, to different stages of the manufacture of nuclei. They allow to illustrate the principle of the manufacture of foundry cores, without the invention is necessarily limited to this precise device.

This device 1 thus schematically comprises a portion 2 called "firing head set" fed powder mixture of sand and binder through a conduit (not shown) into which opens a hopper (not shown). The device also comprises a part 3 called "box cores", a part called "set of drying" 4 (Figure 4) and a part called "ejection system >> 5.

The kernel box 3 is mounted movably along a vertical axis X and along a horizontal axis Z. The drying assembly 4 and the firing head assembly 2 are mounted movably along a horizontal axis Y. The kernel box 3 comprises a heated lower cavity 31, a heated upper cavity 32, forks (not shown), and cavities 34 defined together by the cavities 31 and 32 to define the shapes and dimensions of the cores to be manufactured.

The firing head 2 comprises an injection plate 21 which is in the lower part of the box containing the mixture of sand and binder S, and which is provided with openings in connection with the injection nozzles 22 for supplying the cavities 8 by channels 33 made in the upper cavity 7.

The drying system 4 (Figure 4) comprises an injection bell 41, with an injection point 42 connected to a hot fluid source of dry hot air type (not shown). The injection chamber 42 is able to inject this hot fluid into the cavities 8 via the supply channels 33. Filters 35 on openings of the cavities in the lower cavity allow the drying fluid to be evacuated by retaining the sand in the cavity.

The ejection system 5 comprises ejectors 51 fixed on a movable ejection plate 52 disposed under the lower recess 32.

Figure 1 is a general representation of the coring device with the open core box, at the start of manufacture: the two cavities 31 and 32 are not in contact with each other, the nozzles supply 22 in mixture are not in connection with the channels 33 of the upper imprint 31.

FIG. 2 shows the closed core box 3, in the injection position in the closed cavities 34 of the sand + binder mixture through the nozzles 22 and then the channels 33 opening into openings disposed in the upper cavity cavity recess 31. 34.

Figure 3 shows the core box 3 always closed, with the cavities 34 being filled: this is the step of injecting the mixture S under pressure.

Figure 4 shows the step of removing the firing head and the establishment of the drying system 4 above the upper cavity 31. The hot pressurized fluid is guided from the location where were the supply nozzles 22 through the channels 33 into the cavities 34 to pass through the cores N. It is then discharged through the filters 35 arranged by openings in the lower recess 32. The preferential flows of the fluid flow hot, symbolized by arrows fi in Figure 4, are therefore related to the implantation of the injection nozzles 22.

FIG. 5 represents the step of stopping the blowing of the hot fluid and the opening of the kernel box 3, when the core is sufficiently hardened to be ejected and handled: the cores rest on the lower imprint 32 .

FIG. 6 shows the step of ejecting the N cores, by the ejection system 5, by an upward thrust of the cores by the ejectors 55 supported by the mobile stage 52 in vertical translation.

FIG. 7 represents, according to the invention, an alternative for drying nuclei N: all things being equal, the flow of the hot fluid, as represented by the arrows f2, is reversed by modifying the flow system. drying 4 ', 4 ": the supply of hot fluid is by the system 4', and its evacuation by the system 4". Under the lower recess 32 is added a movable plate 41 'defining a watertight box 42' supplied by a source of hot fluid. Above the upper cavity 31 is used a sealed bell 42 "defined by a plate 41" having a peripheral seal 43 ". Figure 8 is an enlargement of the plate 41 "and will be described with Figure 7.

The injection of fluid is therefore by the box 42 'in fluid connection with the channels 36 formed in the lower cavity and opening into the cavities 34 through openings provided with filters 35, from below. The plate 41 'being traversed by the ejectors 51 through appropriate openings, can be provided with these openings of peripheral sealing means 52 so as to ensure the sealing of the box 42' in these areas.

The hot fluid then goes up through the cores N, through the openings of the plate 42 "provided with evacuation nozzles 43" equipped with teats 44 "whose output section is optionally provided with a filter 45". This plate 42 "associated with the plate 41" defines a waterproof case. The nozzles 43 "are therefore not in the true sense of the injection nozzles, but nozzles for capturing and discharging the hot fluid at the top to the box 42", their filters 45 "ensuring, if necessary, the retention of the sand and binder in cavities 34.

Figure 9 is a variant of Figure 8: all things being equal, it is added to the lower injection system 5 an upper injection system 5 'movably mounted in vertical translation, and comprising ejectors 51' mounted on a movable plate 52 ', and which pass through the plate 42 ". Sealing means (not shown) may be provided to maintain the leaktightness of the evacuation box in the zones traversed by these additional ejectors.

It is possible that one or some of these additional injectors also cross the body of the nozzles 43 "and their filters as shown in FIG. It can also be seen that in addition to the nozzles 43 "(or in their place), simple channels 46" may be provided in the upper cavity 31, possibly equipped with filters 35 in the openings of the cavities 34 into which they open, and which are in fluid connection with the evacuation chamber by a corresponding bore 47 "of the plate 43".

Note that for both variants, it can be provided at the discharge opening of the upper box defined by the plates 41 "and 42" a suction facilitating and accelerating the discharge of the hot fluid.

The invention thus circulates the drying fluid in the opposite direction of the injection of sand + binder mixture. The injection of the fluid is in the example of the invention by conduits in the cavity opening into the cavities through openings equipped with filters. Thus, the step of filling the cavities by injection of the sand is not disturbed; the zones of injection of drying fluid are easily positioned without any negative impact on the quality of appearance of the core, and therefore of the casting, the circulation homogeneity of the drying fluid is improved throughout the porous core.

The advantages of the invention are significant. Thus, it has been observed a time saving in the drying operation which can reach up to 40% of the usual time: the core acquires faster mechanical characteristics sufficient to support the next step of ejection without damage, and this , especially as we inject the hot fluid from the lower cavity, so that we put in contact the hot fluid first with the lower part of the core in the cavity, the one that is subjected most directly to thrust of ejectors.

There is also a gain on the quality of the drying of the core, with a better dehydration thereof, so a more uniform hardening leading to a more solid core, more resistant overall. The core also sees its storage capacity increase, by a greater durability of its mechanical properties.

In addition, the drying can start earlier, because it is no longer necessary to wait for the withdrawal of the injection plate of the sand and the establishment of the injection bell of the drying fluid: the drying can begin as soon as the sand injection tray is removed. By injecting the hot fluid preferably with a progressive pressurization thereof, it is possible to dry earlier without risk of blowing the sand out of the cavities.

The filters positioned both in the blowing openings of the hot fluid and in the discharge openings thereof ensure not only the retention of sand in the cavity but also the absence or the virtual absence of traces of these openings on the core and thus on the resulting casting (which is not always the case of sand injection nozzles). It is even noted that the addition of filters in the openings of the exhaust ducts (which may be the same as the ducts into which the sand injection nozzles open into the injection position) makes it possible to smooth out the defects of aspect created during sand injection.

Note also that it is best to adjust the blowing of the drying fluid by adjusting the blowing pressure, which can be constant or progressive, and that a suction in the evacuation zone also allows a complete adjustment. during drying.

Claims (10)

1. Device (1) coring for gravity foundry, said coring device comprising: - means for constituting cores comprising tools defining molding cavities (34), - supply means powdered compound (s) (S) of said cavities by supply openings, and - drying means of the cores being formed in said cavities (34) by blowing a fluid through blow openings, characterized in that the blow openings are distinct from the feed openings. 2. Device (1) coring according to the preceding claim, characterized in that the blowing apertures are in fluid connection with a fluid chamber (42 ') for supplying fluid. 3. Device (1) coring according to the preceding claim, characterized in that the box (42 ') comprises a plate (41') provided with openings in fluid connection with the blowing openings by ducts. 4. Device (1) coring according to one of the preceding claims, characterized in that the blowing openings are equipped with filter (s) (35). 5. Device (1) coring according to one of the preceding claims, characterized in that the blow openings and the feed openings are arranged relative to each other in the cavities so that the direction of introduction of the powdery materials (S) into said cavities (34) is substantially opposite to the direction of introduction of the drying fluid into said cavities. 6. Device (1) coring according to the preceding claim, characterized in that all the blowing openings are grouped on one edge of the cavity (34), and all the feed openings on an opposite edge. 7. Device (1) for coring according to one of the preceding claims, characterized in that the drying means comprise means for discharging the fluid from the cavities by discharge openings in fluid connection with a box (4 "). ), possibly connected to a suction system. 8. Device (1) cored according to claim 7, characterized in that the discharge openings are also the cavity supply openings (34) and / or are separate openings, preferably provided with filters (35). 9. Device (1) of cored according to one of the preceding claims, characterized in that it has at least two systems for ejection of cores (N) cured, including a system (5) disposed on the side of the openings of blowing and a system (5 ') disposed on the side of the cavity supply openings (34). 10. A method of implementation of the device according to one of the preceding claims, characterized in that feeds powder compound (s) cavities (34) through feed openings, and that in that a fluid is blown into the cavities (34) to dry nuclei (N) being formed in said cavities by blowing a fluid through openings, the injection of the fluid into the cavities in a direction opposite to the injection of the pulverulent compounds.